1. Field of the Invention
The present invention relates to a keyless entry device for locking and unlocking doors of a vehicle by performing a wireless communication between a vehicle-side device and a portable device, and more particularly, to a keyless entry device for accurately judging whether the portable device exists inside or outside a predetermined boundary.
2. Description of the Related Art
A keyless entry device for locking and unlocking doors of a vehicle by performing a wireless communication between a vehicle-side device, which is provided on a vehicle, and a portable device belonging to a user is well known. A passive keyless entry device is also well known in which an automatic communication is performed between the vehicle-side device and the portable device when a portable device is close to the vehicle, and the locking and unlocking operation is performed on a door of the vehicle when a verification of ID, which is uniquely set in each portable device, is performed. Japanese Unexamined Patent Application Publication No. 2002-77972 (U.S. Patent Application No. 2002/0025823) discloses an example of such a keyless entry device.
Particularly, in the passive keyless entry device, judging whether the portable device is located outside or inside the vehicle is an important issue. Because of this reason, a vehicle-side device is provided with a plurality of transmitting antennas on several places of the vehicle. The vehicle-side device judges or determines that the portable device exists inside the vehicle when the portable device receives a radio wave from the transmitting antennas inside the vehicle and judges or determines that the portable device exists outside the vehicle when the portable device receives a radio wave from the transmitting antennas outside the vehicle.
However, in the known keyless entry device, it may be difficult to accurately judge or determine the position of the portable device. For example, even though the portable device is outside the vehicle, a misjudging or determination error occasionally occurs concluding that the portable device is inside the vehicle when the radio wave of the transmitting antenna inside the vehicle is leaked out from the vehicle inside. Conversely, even though the portable device is inside the vehicle, a misjudging or determination error occasionally occurs concluding that the portable device is outside the vehicle when the radio wave of the transmitting antenna outside the vehicle is leaked to the vehicle inside. If a transmitting power of the radio wave from the transmitting antenna is reduced in order to prevent the leakage of the radio wave, occasionally, the portable device can not receive the radio wave even though the portable device is inside the vehicle. This is also one factor that causes the error by misjudging.
On this account, the present applicant contrives a keyless entry device configuring a data group of a vehicle inside and a data group of a vehicle outside by previously obtaining information of an intensity from a plurality of transmitting antennas in each case of a portable device in accordance with the vehicle inside and the vehicle outside distinguished by a boundary between the inside and outside of a vehicle, detecting signal intensities from the plurality of transmitting antennas for judging a position of the portable device, and judging which side of data groups of the vehicle inside or the vehicle outside approximates to the data by using a Maharanobis distance calculation. Further, the boundary which is a reference judging a position is not limited to the boundary between the inside and outside of the vehicle.
However, in order to configure a data group used in a Maharanobis distance calculation, a plurality of data is acquired. Accordingly, the data that is previously acquired is taken from only the vicinity of the boundary, while the data of the position apart from the boundary is not acquired. Using this method, it is possible for the vicinity of the boundary to judge or determine a position very accurately by the Maharanobis distance calculation, but there is a problem in that it is not easy to judge or determine a position very accurately, even if the position is by any side of the vehicle, when the position is greatly apart from the boundary. The reason is, regarding to the position greatly apart from the boundary, a ratio of difference between a Maharanobis distance for the data group of the vehicle outside and a Maharanobis distance for data group of the vehicle inside decreases. To judge or determine this accurately, it is also possible to consider obtaining data by additionally including the position greatly apart from the boundary, but there is a problem that the number of processes increase in excessively high rate, and the data rate in the boundary point relatively decreases, whereupon there is another problem that the accuracy in a principal boundary position is reduced.
In the keyless entry device contrived by the applicant in the past, even though the portable device is located at any position, it operates to judge or determine by using the Maharanobis distance. Consequently, it takes too much time to judge or determine the position from the viewpoint of a whole system operation.